1. Technical Field of the Invention
This invention relates to bearing protectors, especially, but not exclusively, of the non-contacting labyrinth seal type, and their use in rotating equipment, especially equipment which has a particularly large shaft or is difficult to disassemble/strip down.
2. Description of the Prior Art
An example of a piece of rotating equipment which is difficult to disassemble is a centrifugal pump with bearing assemblies supporting the rotating shaft.
In such equipment, each bearing arrangement typically consists of at least one bearing housed in a bearing chamber. The bearing is lubricated and sealed between the rotor to stator interface to prevent the ingress or egress of a fluid or solid to or from the bearing cavity, since such unwanted material results in the deterioration of equipment life.
Bearing protectors are often also referred to as bearing seals or bearing isolators. Such seals have applications beyond the protection of a bearing in rotating equipment. Accordingly, while reference will be made below to bearing protectors, it should be understood that this term is used, as far as this invention is concerned, in connection with such wider applications.
During pump operation, bearing seal components may deteriorate to such an extent that they must be repaired. Often, it is not economically feasible to take a pump out of production, disassemble it and remove the interference fitted bearings in order to fit new bearing seals. This therefore creates a dilemma for the pump operator, since the deteriorated seals will accelerate the probability that debris and moisture enter the bearings and cause major failure/cost.
The purpose of a bearing protector is to prevent the ingress of fluid, solids and/or debris from entering a bearing chamber. Equally, bearing protectors are employed to prevent the egress of fluid or solids from a bearing chamber. Essentially, their purpose is to prevent the premature failure of the bearing.
Non-contacting bearing protectors can be of repeller or labyrinth configuration. Reference is made to our co-pending labyrinth seal bearing protection application, United Kingdom Patent Application No. 0415548.7, which defines a substantially non-contacting bearing protector with a static shut-off device.
In a non-contacting bearing protector, the rotating component typically has a complex outer profile which is located adjacent and in close radial and longitudinal proximity to a complex inner profile of the stationary component. Together these complex profiles, in theory, provide a tortuous path preventing the passage of the unwanted materials or fluids.
Split seals are used in applications where the rotating equipment is difficult to disassemble. Such seals comprise two parts, a stator and a rotor, both of which are radially split about their central axis, so that they can be radially mounted over a shaft compared to the more traditional longitudinal mounting on the shaft of a conventional non-split seal design.
Conventional labyrinth seal technology indicates that the closely positioned longitudinal counter rotational members are substantially parallel to each other and run perpendicular to the centreline of the shaft. As labyrinth seals are non-contacting designs there is a natural leak path through the rotor to stator interface. A radially split labyrinth, thus, has further leak points, given the nature of the design. In order to reduce leakage potential, radial, substantially male elements of the rotor can protrude longitudinally and mesh into substantially female radial recesses of the stator, thereby creating a tortuous path for fluid to pass. Unfortunately, a radially split labyrinth seal has to have radial access so that the stator can be assembled over the rotor while, in situ, on the shaft. Intermeshing longitudinal protrusions between the rotor and stator render impractical radial assembly unless there is sufficient longitudinal space available in the equipment for this operation to be done in a longitudinally spaced position, i.e. with the rotor and stator separated. At least one longitudinal end of the stator and/or rotor assembly must be open and this creates a potential leak path for contaminants to enter.